This invention relates generally to electroplating apparatus and methodology, and more specifically relates to the electroplating with gold of electronic components or the like.
Gold, within recent years, has become a very important part of the electronics industry. Among those properties recommending its use therein, are its relative unalterability, high solderability and low contact resistance. In the semi-conductor field, gold has furthermore found favor because of its ability to readily form an eutectic alloy with silicon and germanium. In the latter connection it may be noted that most headers or packages for diodes, transistors, and integrated circuits are gold plated as a preparation for the mounting or attaching of semi-conductor devices Such components are exemplified by the well-known line of TO-5 and TO-8 multi-lead headers. Such headers consist of an eyelet of Kovar metal to which several insulated Kovar leads are attached, and sealed in glass.
In accordance with known principles in the art, headers of the foregoing type have, in the past, been plated (among other methods) by so-called barrel plating techniques -- that is, by subjecting such articles to electroplating while a plurality of articles tumble in a barrel. These barrel techniques, however, have many important drawbacks, numerous of which are recognized in the art. For example, where headers or the like are thus plated, it is found that many leads do not make electrical contact with the remainder of the load. Where such conditions obtain during the plating cycle, the portion of the lead closest to the anode becomes cathodic. Such leads become bipolar, and at the anodic portion of the leads problems can arise in that the gold may redissolve anodically, and as well base metal can be attacked to expose bare spots. Where the tumbling action is markedly inadequate these problems can become quite severe. In the past these problems have partially been overcome by incorporating mechanical means for improving electrical conductivity through the load. Such means have taken the form of metal particles or metal shot. Unfortunately during plating operations the shot itself becomes gole plated, resulting in the loss of gold and attendant increase in the cost of plating the desired objects, that is, the headers, etc.
Within recent years, particularly because of the soaring price of gold, it has furthermore been increasingly appreciated that barrel plating techniques (and as well, common rack plating techniques) are exceedingly wasteful of the gold itself. If one considers, for example, the most common use of barrel plating in the electronic industry, i.e. the plating of the aforementioned headers, it will be appreciated that basically one is only interested in providing a plating at the die-receiving face thereof, and at the contact connections for the header leads which are present at the said face. Barrel plating techniques, however, are such that the entire header is plated with gold -- including all electrically conductive, accessible portions thereof. Furthermore, since barrel plating is based upon the development of multiple electrical contacts among the tumbling components, it is basically a statistical process, this is to say that different components in a tumbled load may be subjected to markedly different plating times. In order to achieve a desired mean plating thickness, it is therefore necessary to grossly overplate, in order to assure that all of the individual components in the batch receive adequate plating, it is frequently necessary to overplate many of the components by as much as 10% to 20%. This is obviously a further waste of the precious gold material.
In the copending patent application of Frank J. Johnson, filed July 13, 1973, and entitled "Apparatus and Method for Continuous Selective Electroplating", Ser. No. 379,113, now U.S. Pat. No. 3,904,489 which application is assigned to the same assignee as the instant application, there is disclosed apparatus and method which are highly effective in overcoming the foregoing problems of the prior art. The said apparatus in particular, is adapted to enable continuous electroplating of selected portions of discrete electronic components or the like. In accordance with the Johnson apparatus a plating belt adapted for carrying electroplating solution on the surface thereof, is continuously moved through an electroplating station. Electroplating solution is applied to the belt at a point in the progression thereof which is upstream of the electroplating station, as for example, by passing the belt (which may be in the form of a loop) through a reservoir for the solution. The discrete components to be selectively electroplated are arrayed in a line, and are conveyed across the surface of the moving plating belt, with the portions of the components to be plated in contact with electroplating solution on the belt. The direction of movement of the components is generally counter to the movement of the plating belt, and is more specifically at a skewed direction with respect to the direction of movement of the said belt. The angle of skewing in relationship to the speed of progression of the plating belt and of the components, is such that the trace of each component upon the plating belt continuously overlies fresh electroplating solution; which is to say that the various components are continuously wiped by fresh electroplating solution. A D.C. electrical potential appropriate to enable the desired electroplating, is applied between the component portions to be plated and the backside of the plating belt.
In accordance with the concepts set forth in the said Johnson application, the means for conveying the discrete components through the electroplating station preferably comprise a pair of parallel moving conductive belts, the spacing between the belts defining openings for supporting the components to be plated. The portions selected for plating therefore project beneath the conductive belt during passage through the station. As the borne components approach the station in Johnson an electrically non-conductive gripper belt passes atop the components as to sandwich same with the pair of conducting belts underlying the component. In order to effect electrical contact with the wire-like leads which extend upwardly from the conveyed components, a further movable belt, provided with a resilient conductive surface contacting the leads, is made to move with the conductive and gripper belts through the electroplating station.
While the aforementioned Johnson apparatus has, as indicated been found effective for its purposes, it has nevertheless been observed that the apparatus is less than ideal as respects performance and reliability characteristics thereof. A principal difficulty arises from the conveying system, which is overly complex -- as regards its basic mode of transporting the said components. The parallel moving belts, for example, require frequent adjustment, and relatively minor imperfections in the belts or in their relative spacing or rates of movement, can lead to lack of uniformity in the plating of individual components. It is, furthermore, difficult with the relatively flexible Johnson conveying arrangement, to provide and maintain accurate spacing from the solution applicator belt as the components pass through the plating station; and indeed the components may even undergo wobble about their longitudinal axis due to the absence of restraint against such motions. Similarly, application of electrical potential to the conveyed workpiece is effected in relatively complex fashion -- which can comprise an additional impediment to dependability of performance.
In accordacne with the foregoing, it may be regarded as an object of the present invention to provide apparatus enabling on a mass production basis, the electroplating of selected portions of electronic components or the like, thereby eliminating the waste of plating metals previously occurring where the said components were subjected to gross plating thereof.
It is a further object of the present invention, to provide apparatus enabling selective electroplating of electronic components or the like with gold, or similar precious metals, which apparatus enables such operations on a continuous basis, which results in platings of excellent quality and carefully controlled thicknesses, and wherein the uniformity of plating thickness and quality from piece to piece is correspondingly high.
It is a yet further object of the present invention, to provide apparatus for selective electroplating of electronic components or the like, which is of improved dependability of operation in comparison to prior apparatus, and which is greatly simplified in comparison to such prior apparatus, thereby enabling greatly increased effectiveness in realized results.